Currently, to improve input/output performance of a disk system, for example, to reduce a request response time and increase a throughput rate, in most storage systems, a cache technology is used at an upper layer of the disk system to meet a performance improvement requirement.
In a conventional storage system, a database system generally uses a DRAM (Dynamic Random Access Memory) as a cache medium. The DRAM has advantages of read/write balance and write durability. There is no need to consider a write count of the DRAM, and data can be frequently written into the DRAM.
To reduce a cost of a cache medium, increasing storage systems use an SSD (Solid State Drive) as the cache medium. The SSD has advantages of a greater capacity, a lower cost, and non-volatility. However, the SSD has a limited erase count. When the SSD is managed by using a conventional cache replacement algorithm (such as an LRU), because the cache medium lacks a drive data update, a miss of a new read request causes a data block in the SSD to be deleted. If new read requests are constantly missed, data blocks in the SSD are constantly kicked out, and a retention time of data blocks in the SSD is extremely short. However, these kicked-out data blocks may be rewritten into the SSD after a specific period of time. Consequently, frequent data erase operations can reduce service life of the SSD and increase a cost and maintenance difficulty.